High intensity, gas discharge lamp dimmer system

ABSTRACT

A dimmer circuit for a high intensity discharge lamp system that controllably reduces the current through such lamps with consequent reduction in illumination thereof without causing cessation in the lamp current at any time. The circuit is controllable for changing the rms value of the lamp current without changing the slope of the lamp current as it goes through zero from one polarity to the other. A triac bypasses one of two ballast elements, connected in series, for varying the angles of conduction of the triac to control the rms value of the lamp current. The triac is fired from a gate source voltage in phase with line voltage, the amplitude of the gate source voltage being controlled by a zener diode, or other gate-signal control, device to properly time the turning on of the triac in relation to the lamp current. The zener diode, or other gate-signal control, device also prevents the triac from remaining conuctve past a time when there might be opposite polarity ballast-element voltage and lamp current.

United States Patent Snyder June 11, 11974 Primary Examiner-Palmer C. DeMeo [75] Inventor: Carl R. Snyder, Alief, Tex. f iF E p d h I 1mmer c1rcu1t or a 1g mtensity 1sc arge amp [73] Asslgnee' New York system that controllably reduces the current through [22] Filed: Apr. 23, 1973 such lamps with consequent reduction in illumination thereof without causing cessation in the lamp current [21] Appl. No., 353,793 at any time. The circuit is controllable for changing Relat d US, Application Data the rms value of the lamp current without changing [63] Continuation of Ser. No. 238,800, March 28, 1972, the Slope the lamp current as through Zero abandoned. from one polarity to the other. A triac bypasses one of two ballast elements, connected in series, for varying 52 us. 01 315/194, 315/195, 315/254, the angles of conduction of the triae to centre! the 315/258, 315/272, 315/283, 315/297, 315/310 rms value of the lamp current. The triac is fired from [51] Int. Cl. HOSb 41/38 a gate Source Voltage in PhaSe with line Voltage the [58] Field of Search 315/194, 195, 254, 258, amplitude of the gate seuree voltage being controlled 315/272, 7 233 7 310, DIG. 7 by a zener diode, or other gate-signal control, device to properly time the turning on of the triac in relation 5 References Cited to the lamp current. The zener diode, or other gate- UNITED STATES PATENTS signal control, device also prevents the triac from remaining conuctve past a time when there might be opposite polarity ballast-element voltage and lamp cur- 3:700:962 10/1972 Munson 315/283 x rent 23 Claims, 12 Drawing Figures L/NE I6 48 42 V VW F I COMMON PA'TENTEDJIIII 1 1 m4 18-16794 saw a or e FULL LAMP CURRENT LA MP VOL TA GE DIM LAMP CURRENT FULL ON STATE D/M STATE FIG. 2a

I; /F TRIAC NOT FIRED I] BEFORE FIRING TR/AC I1 AFTER TR/AC COMMUTA TES 1 AFTER F/R/NG TR/AC 6 IS BETWEEN OAND 85 LUMENS PATENTEDJIIIH m4 ,SHEEI 3 0f 6 14 12 Q W cum GATE FIG. 5 L3 ,START/NG cow LAMP ON NORMAL BALLAST TURNED q ONIN a DIM x STATE 20- FIGS TIME PATENTEDJUIIH m4 38-16394 saw a nr 6 LINE GA TE 29a 29b 29c 28c 28b 28c 32a 32b 3 32c 20c 20b 20c COMMON FIG. 8

FIG. 9 FIG. 10

L/NE LINE GATE GATE COMMON COMMON HIGH INTENSITY, GAS DISCHARGE LAMP DIMMER SYSTEM This application is a continuation of application Ser. No. 238,800, filed Mar. 28, 1972, and now abandoned.

FIELD OF THE INVENTION This invention relates to lamp dimming circuits and more specifically to such dimming circuits that are uniquely applicable to high intensity discharge lamps, such as mercury vapor lamps having two electrode terminals and no heater.

DESCRIPTION OF THE PRIOR ART Mercury vapor and other metallic-additive high intensity discharge (H.I.D.) lamps have found widespread acceptance in lighting large areas, such as warehouses, gymnasiums, and the like, primarily because of their relatively high efficiency and low maintenance when compared to incandescent lighting systems. There has been general approval of such system for large area illumination in spite of the fact that heretofore, there has been no satisfactory method of reducing the illumination during periods when full illumination has not been desired. When it is desired to reduce illumination in an area normally lit by a high intensity discharge lamp system, it has been necessary either to completely turn off some of the lamps in the system or to switch to an auxiliary incandescent or fluorescent lamp system.

Switching off some lamps and not others gives unsatisfactory full-range control and increases the complexities of the system by requiring additional wiring, switching equipment, etc. Having to provide an auxiliary system likewise greatly increases the complexities of the overall lighting system. In addition to additional wiring and switches, additional fixtures, lamps and even power handling equipment is required when an auxiliary system is employed.

Heretofore, it has not been believed possible to incorporate a dimming control system directly into a high intensity discharge lamp network. First, it has widely been supposed that when power consumption is reduced in a high intensity discharge lamp, electrode sputtering would result, which would cause damage to the environment within the lamp. Such damage would greatly reduce the life of the lamps and also cause undesirable flickering. Second, the existing dimming circuits for incandescent and fluorescent lamps would extinguish a high intensity discharge lamp. This is because such circuits actually turn off the lamps with which they operate for short periods of time during each operating cycle. Although this mode of operation is acceptable for incandescent and fluorescent lamp operation, it would not be acceptable for operation with high intensity discharge lamps. Such a lamp, once turned off, requires a relatively long cooling period after extinguishment before it can be restarted.

It has been discovered, however, that by employing a dimmer circuit that does not cause off time during half cycles in lamp current, but which is controllable for changing its rms value without changing the time or the slope with which it goes through zero when changing its polarity, it has been found that a practical high intensity discharge lamp system may be dimmed. The reduction of current through a high intensity discharge lamp can be effective in providing dimming without damage to the lamp by bypassing current around an accompanying ballast element and hence achieving the reduction of lamp current for short operating periods, provided such operation does not operate to cause current flow and a voltage drop of opposite polarity across this accompanying ballast element.

It is therefore a feature of this invention to provide dimming apparatus incorporated directly as part of a metallic-additive high intensity discharge lamp system for controllably reducing the illumination from such lamps.

It is another feature of this invention to provide dimming apparatus for a metallic-additive high intensity discharge lamp system that does not shorten the life of the lamps in such system compared to operation under full-power conditions.

SUMMARY OF THE INVENTION A preferred embodiment of the present invention comprises, in combination with a single high intensity discharge lamp, circuitry operating with two ballast elements connected in series with the lamp, the series combination being connected across a single phase ac distribution line and power common. One of the ballast elements is bypassed by a triac or other device. The gate terminal of this triac is operated by a phase controllable clipped voltage that operates the triac within predetermined time boundaries. That is, the triac may be turned on only during periods when the reactor voltage (voltage across the triac and the ballast element) and the current through the lamp (and hence the ballast element and the triac if it is conducting) are of the same polarity. Thus, a bypass for current through the lamp is provided which continues after the reactor voltage has changed polarity with respect to such lamp current.

The timing of the gate firing voltage to the triac is provided by a circuit including a second triac a bidirectional switch in the gate circuit of this second triac, and bidirectional zener diodes connected in series with the power terminals of the second triac. The timing of the bidirectional switch operation is determined by a variable resistance in series with the control voltage, in phase with the line voltage. If the threshold value of the bidirectional switch is reached very fast by a low resistance setting of the resistance, then the switch, second triac and zener diodes will turn on to provide a gate voltage to the first triac very close to the time the lamp current crosses its zero value from one polarity to the other. On the other hand, a high resistance setting of the variable resistance for the gate source voltage delays the occurrence of the switch threshold event and the subsequent operations until a later time.

Turnoff of the gate to the first triac is provided by the excursion of the gate signal voltage sine wave to a value below the zener diode values. This occurs before the reactor voltage changes polarity with respect to the lamp current. A zener diode pair in combination with a fixable gate source voltage is especially advantageous as a source for the gate voltage to the inductively loaded first triac since during their respective periods of conduction, a fixed cutoff of gate voltage can be achieved such that no gate signal can be applied which is out of phase with lamp current.

The sequencing of this bypass means around one of the ballast elements maintains a non-injurious phase relationship between current and voltage for lamp operation.

The control for the gate source voltage may be isolated from the high voltage distribution line as a safety feature via transformer connections and the variable control may be a simple potentiometer.

BRIEF DESCRIPTION OF THE DRAWINGS So that the manner in which the above-recited features, advantages and objects of the invention, as well as others which will become apparent, are attained and can be understood in detail, more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof which are illustrated in the appended drawings, which drawings form a part of this specification. It is to be noted, how-' ever, that the appended drawings illustrate only typical embodiments of the invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

In the drawings:

FIG. 1 is a schematic diagram of a preferred embodiment of dimming apparatus in accordance with the present invention.

FIG. 2 is a waveform diagram showing the amplitude and phase relationships existing in the lamp voltage and the range of bright and dim currents of the circuit shown in FIG. 1.

FIG. 2a is a waveform diagram illustrating relative currents to achieve full and dim conditions.

FIG. 2b is a waveform diagram illustrating summing of currents to achieve an intermediate current value between full and dim.

FIG. 3 is a schematic illustration of an alternative circuit for producing gate source voltage.

FIG. 4 is a waveform diagram showing the amplitude and phase relationships existing in various important voltages and currents of the circuit shown in FIG. 1.

FIG. 5 is a lumens versus time diagram of a typical lamp operation, showing the effects of operation in conjunction with the circuit of FIG. 1.

FIG. 6 is a wattage versus time diagram of a typical lamp operation, showing the effects of operation in conjunction with the circuit of FIG. 1.

FIG. 7 is a schematic diagram of a preferred embodiment of the invention connected in a three-phase power distribution system, with single element control.

FIG. 8 is a partial schematic diagram showing the connection of multiple lamp fixtures in a single control system in accordance with the present invention.

FIG. 9 is a partial schematic diagram showing the employment of parallel ballast inductors connected in series with a high intensity discharge lamp.

FIG. 10 is a partial schematic diagram of a high reactance autotransformer ballast, including a series connected dimmer reactor therewith and its bypass triac.

DESCRIPTION OF PREFERRED EMBODIMENTS Now referring to the drawings and first to FIG. 1, high intensity discharge lamp 10 is connected in series with two inductive ballast elements 12 and 14, the en tire combination being connected between line 16 and common 18. Gated bypass means in the form of triac 20 is connected across element 14, main terminal one 22 of the triac being connected to the line and main terminal two 24 being connected to a junction point between the two elements. Gate terminal 26 is connected to resistor 28 and is connected to fuse 29, which is connected with gate fuse 30 and in multiple with the gate connection of other lamp and ballast circuits. A power factor correction capacitor 32 is connected from line to common across the entire combination just described.

When triac 20 is conducting to form a complete bypass around element 14, a maximum amount of current (designated full lamp current in FIGS. 2 and 4) flows through lamp 10. On the other hand, when triac 20 is not conducting, then the minimum amount of current flows through lamp 10, as indicated by dim lamp current curve in FIGS. 2 and 4. By allowing triac 20 to conduct for part of the cycle as shown by the dash lines in FIG. 2, then the current through lamp 10, and, hence the illumination therefrom, may be varied between the dim lamp current and full lamp current values. A short period of conduction by triac 20 creates a curve 101, a little longer conduction period like curve 103 and still longer period like curve 105. It is apparent, therefore, that merely controlling the period of triac 20 conduction will achieve controllable illumination of the lamp 10.

Control of the conduction of triac 20 is accomplished by the controllable gate voltage means connected to gate fuse 30. To understand the operation of this circuit, some additional phase relationships have to be appreciated, which can best be shown by referring to FIG. 4. The voltage across element 14 (reactor voltage) is leading the lamp current by approximately and is also leading the line voltage by approximately 30.

It is readily apparent that triac 20 should not be rendered conductive until the current through and the voltage across element 14 are both of the same polarity, either both positive or both negative. Considering the positive polarity cycles, the current through element 14 does not go positive until point 107. At this time, the reactor voltage is already positive. At point 109, the reactor voltage goes negative, although the current through indicator 14 is still positive. The range 111 of time over which a gate voltage may be applied is hence determined as being the time between points 107 and 109.

It is again well known that the gate pulse to a triac controlling an inductive load is desirably a continuously applied gate voltage, rather than an instantaneous spiked pulse. Again referring to FIG. 1, bidirectional voltage regulating means in the form of cathode-tocathode zener diodes 33 and 34 are connected to gate fuse 30. Connected in series with zener diodes 33 and 34 are main terminals one and two of triac 36, the entire combination being connected through components discussed hereinafter to line 16 via a secondary 38 of power transformer 40. Capacitor 44 is provided for transient suppression. It is readily apparent that the gate voltage has for its source from secondary 38 a voltage which is in phase with line voltage 16. This voltage is labelled gate source voltage on FIG. 4.

Connected to the gate terminal of triac 36 is a semiconductor, bilateral switch 42, which has very low forward voltage drop on the order of one volt when a predetermined threshold is exceeded in either polarity. Bi-

lateral switch 42 is a part of a conventional double time constant control circuit including capacitors 45 and 46 and resistor 48. This control circuit is of the type manufactured and sold by RCA under manufacturers designation AN 3697. Its input is derived from the secondary of a transformer 50. Transformer 50 is supplied controlled voltage via secondary 54 of power transformer 40 and its related components. Hence, the voltage supplied to the control circuit is in phase with the line voltage.

In operation, when the threshold of switch 42 is exceeded by the application of the control voltage from secondary 54 and its related components, a gate is supplied to triac 36 to cause conduction thereof. Triac 36 conducts when the gate source voltage exceeds the zener diode voltage of zener diodes 33 and 34. Such a voltage provides an ample gate drive for triggering gate 26 of triac 20.

Referring now to FIG. 2a, there is shown a waveform illustrating summing of current taken at points I, (through reactor I4) and I (through triac 20) in FIG. 1. If triac 20 is not gated on, No. I current flows and the only current flow through the lamp (I is L. This is reflected as the dim state. On the other hand, if triac 20 is gated on during the entire time, then the entire current is bypassed around reactor 14 and through triac 20. Hence, 1 becomes essentially zero and I equals 1 as shown by the full on state curve.

If traic 20 is gated on to an angle 0 following the occurrence when current through the lamp becomes positive, a triac current 1 will be generated which is added to reactor current I,, as shown in FIGS. 2 and 2b. At the same time, current I that had been rising assumes essentially a steady state l until the time that triac 20 is no longer conducting. Hence, current I relative to time is equal to 1, before the triac is fired, then equal to l plus I while the triac is conductive, and then is equal to 1 again after triac 20 commutates.

As shown in FIG. 4, it is necessary that the gate voltage is prevented from continuing past the gate cutoff point. Although the gate voltage may be readily controlled by zener clipping as indicated above and as illustrated in FIG. 4, it is deemed within the scope of the present invention to provide other appropriate circuit means for controlling the gate voltage to prevent voltage past the gate cutoff point from energizing the triac. One such means may conveniently take the form of a Y connected power source circuit, as illustrated in FIG. 3. It may be observed that lamp and ballast elements I2 and 14 are connected in series between two of the lines of the Y, namely, L and L As with the circuit shown in FIG. 1, element 14 is bypassed by triac having a gate resistor 28 and a fuse 29. Fuse 29 is connected to the gate connection lead, which may be connected to parallel lamp and ballast connections as with the other embodiments. This connection is also connected to a network 80 in leg L of the Y. Network 80 may be identical to the circuit shown in FIG. I from transformer 40 through fuse 30 that is connected to the gate connection of the circuit, except there are no zener diodes 33 and 34 in network 80. For convenience, capacitor 44 is shown separately connected, although it is really a part of network 80. The secondary of the transformer in network 80 in leg L, of the Y provides a voltage which leads the voltage from L to L by 30. By employing this voltage as a gate source voltage for gating on triac 20, clipping of the voltage becomes unnecessary. Other appropriate circuits may be provided within the scope of this invention to produce a gate source voltage that appropriately leads the line voltage, which may be some angle other than 30. By selecting the time and amplitude of the gate source voltage it is possible to eliminate clipping.

Once conduction of triac 20 is started, the gate source voltage must return to zero before the reactor voltage reverses polarity. This is accomplished in the circuit shown in FIG. I by the zener diodes cutting off when the gate source voltage applied thereto falls below a predetermined value, as shown in FIG. 4. Again a voltage leading the line voltage by approximately 30 may be used for the gate source voltage thereby eliminating the zener diodes 33 and 34.

The setting of the turn on time of triacs 36 and 20 is accomplished by the setting of resistor 52, a variable potentiometer connected between secondary 54 of transformer 46 and the primary of transformer 50. The time of turn on is determined when the amplitude of the voltage applied to switch 42 reaches its turn on, or breakdown, value.

The turn off point of the zener diodes does not vary. It is apparent, however, that the shutting off of the zener diodes and hence the gate voltage to triac 20 does not instantaneously render triac 20 nonconductive. The inductance of elements 12 and 14 causes current to continue through triac 20 until the current commutates. The current through lamp I0, after such commutation, is only current through reactor 14 as illustrated in FIGS. 2, 2a, 2b and 4.

There are several operational characteristics of metallic-additive high intensity discharge lamps that prevent heated cathode fluorescent lamp dimmer circuits from being employed therewith, although some instant start fluorescent lamp dimmer circuits may have some applicability to such lamps. For example, with the rapid start fluorescent lamps employing heaters, it is not necessary to consider possible extinguishment of the lamp. Even with the so-called instant start fluorescent lamps not employing heaters, low pressure operation is such that they still do not have the stability problems of the high intensity discharge lamps. If the lamp is extinguished momentarily because of current reversal, the fluorescent lamps relights whereas the high intensity discharge lamp must cool to reduce pressure before it may relight. Hence, the critical timing problem between lamp current and reactor voltage, while still permitting the current amplitude to vary, is unique with the high intensity discharge lamp application.

It has been shown in tests that lamp electrode sputtering occasioned by low current, and hence low arc tube pressure, will not occur when the dimmer circuitry of the present invention it utilized, and hence there will be no deleterious effects to the lamps.

Actual performance characteristics using the circuit hereinabove described have been measured, resulting in the curves shown in FIGS. 5 and 6. The bottom curve shown in FIG. 6 shows the gradual increase in lumens and wattage when the lamp is turned on in the dim state. The lumens reach a steady state value of about 2 percent and the wattage reaches a steady state value of about l0 percent. I

With a high intensity dischage lamp operating at full rated value, turning the lamp to its dimmest operation results in a reduction in lumens to about 20 percent (reduction in watts to less than 30 percent). As the lamp cools further, the voltage across the lamp gradually decreases with an accompanying decrease in lumens and wattage. Twenty minutes after being placed on full dim, the lumen value decreases to about two percent of initial lumen value and the wattage reduces to about percent of full wattage.

Turning the lamp to full power after stabilization at full dim shows the lamp instantaneously jumps to above 30 percent of lumens percent of wattage) and within four minutes was at full value of lumens and wattage. For comparison, a cold lamp does not instantaneously rise to percent of lumens, but as shown in FIG. 5 does so only after about two-three minutes.

FIG. 7 shows a connection of the control circuit in a three-phase power distribution system. Lines L L and L designate respective lines of the three-phase system, each line being connected to a separate power transformer 210, 212 and 214. The remainder of each respective control circuit is similar to that shown in FIG. 1 for a single phase system with the exception of the control network for changing the amplitude of the control voltages firing individual diacs 42a, 42b and 42c.

For example, in the first phase network, a secondary of transformer 210 is connected to an ac terminal of full wave bridge rectifier 216 comprising diodes 218, 220, 222 and 224. Bridge 216, and bridges 228 and 230, is commercially available as a single component, but for clarity of connection and operation, the four diodes comprising the bridge is illustrated. The other ac terminal of bridge rectifier 216 is connected to isolation transformer 226. In like manner, a full wave bridge rectifier 228 is connected in the second phase network and a full wave rectifier 230 is connected in the third phase network.

The dc terminals of bridges 216, 228 and 230 are connected in additive series, the series combination being connected in series with a limiting resistor 232 and a variable resistor 234. It is apparent that changing the value of resistor 234 changes the voltages across each transformer 226 and the corresponding transformers 236 and 238 in the second and third phase networks. Hence, by a single variable resistance control, dimming is effected in each of the three phases. It may also be noted that the control potentiometer may be located remotely from the other components in the control network. Of course, if desired, each of the phases may be separately controlled in the manner described above for the circuit shown in FIG. 1. v

Finally, it may be noted that each of the phases shown in FIG. 7 may be connected to a series of fixtures in the maner shown in FIG. 8. Each lamp 310, 312 and 314 has associated therewith its own series connected ballast elements, a gated triac bypassing one of the ballast elements, and a power factor correcting capacitor.

Power factor capacitors have the same function in the dimmer circuit application as they do in connection with conventional gaseous-discharge lanp ballasts (it is not uncommon for power factor capacitors to be built internally with the ballast elements). For example, the power factor equals approximately 90 percent when the lamps are full on. As the power to the lamps is decreased, the inductive volt/ampere relationship is modified while the capactive volt/ampere relationship re mains the same. This causes the power factor to go from approximately 90 percent lag to approximately 50 percent lead although under no condition will the line current exceed the normal operating line current with the lamps full on. The same control simultaneously provides gate control to each of the bypass triacs 20 thereby dim each lamp in the multiple connection.

As an alternative to the use of series related reactors or ballasts as illustrated in FIGS. 1 and 8, it may be convenient to connect the ballast reactor elements in parallel for the purpose of modifying the inductive devices of the circuit or to limit the required current carrying capacity of the triac. For example, as illustrated in FIG. 9, reactors or ballasts 320 and 321 are shown to be connected in parallel across the line and common conductors and are disposed in series with a gaseous-discharge lamp 322. A power factor capacitor 323 bridges the ballast-lamp combination.

Ballast 321 is connected in series with a triac 324 having a gate terminal 325 connected to the gate conductor. A current limiting resistor 326 is disposed in the gate terminal lead for the purpose of limiting application of current to the gate terminal of the triac.

If the multiple connection arrangement as illustrated in FIGS. 1 and 8, which may be referred to for convenience as the series connection, are used, reactor or ballast element 12 would carry the full lamp current and would be a standard ballast for a given lamp and line voltage. Triac 20 would carry full lamp current when the dimmer was full on. Triac 20 would have voltage blocking requirements determined by the ratio of the impedance of reactors 12 and 14.

As indicated, reactor or ballast element 12 must be capable of carrying the entire lamp current. Because the series-related ballast element 14 is bypassed upon triggering of a triac 20, ballast element 12 may be expected to be of heavier construction than that of ballast element 14, which, at least for much of the time does not carry full lamp current. For example, for operation in dimmer circuitry for a conventional high intensity gaseous-discharge lamp, identified at 10, it may be necessary for the greater current carrying ballast element 12 to be of -ohm value (l440 volt amps) while the impedance value of the ballast element 14 may be on the order of 245 ohms (550 volt amps). The 90-ohm ballast would obviously be of much more expensive nature than the 245-ohm ballast.

If the multiple connection arrangement as illustrated in FIG. 9, which may be referred to as the parallel" connection, is used, reactor 320 would carry dim current and reactor 321 would carry the remaining current for full operation. Hence, neither would have to be as large as standard ballasts. Triac 324 would only carry the current through reactor 321, but would be required to block full line voltage.

In ballast design, the more critical design parameter is normally the current-carrying capacity of the elements. Hence, it may be seen that the ballast arrangement in the dimmer system may be altered to provide a more economical arrangement without sacrificing efficiency.

Finally, yet another ballast arrangement is illustrated in FIG. 10. In this arrangement, high intensity discharge lamp 410 is connected across high reactance autotransformer ballast 412 and aseries-connected dimmer reactor 414 is connected between the two segments, primary 413 and secondary reactance 411, of the autotransformer. The junction between this dimmer reactor 414 and primary 413 of the autotransformer is connected to the line. A triac 420 bypasses the dimmer reactor, the gate connection thereof being connected to the gate voltage source as with the previous embodiments. A power factor correcting capacitor is connected across the primary winding.

In operation with triac 420 rendered non-conductive, line voltage is applied to secondary 4111 of the autotransformer via its primary 413 and via reactor 4M. When triac 420 is rendered conductive for short periods of time as previously discussed, current in the secondary of the autotransformer is increased as reactor 414 is bypassed, thereby increasing the current through lamp 410, as with the other embodiments. When the gate source voltage is removed from triac 420, the impedance of reactor 414 and secondary reactance 411 sustains conduction of triac 420, again in the manner illustrated for the other embodiments in FIGS. 2 and 4.

While particular embodiments of the invention have been shown and discussed, it will be understood that the invention is not limited thereto, since many modifications may be made and will become apparent to those skilled in the art.

What is claimed is:

1. In combination with a high intensity gas discharge lamp, a dimmer circuit for controlling the brightness thereof, comprising ballast means connected to the lamp and connectable to an ac power distribution line,

said ballast means including a reactor portion, gated bypass means for providing at least partial bypass of current around said reactor portion of said ballast means, and

controllable gate source voltage means operably connected to said gated bypass means for controllably rendering said gated bypass means conductive, and thereby bypassing said reactor portion of said ballast, through a time range when the current through said reactor portion and the voltage thereacross are of the same polarity.

2. A dimmer as set forth in claim 1, wherein said ballast means includes a first ballast element in series with said lamp and wherein said reactor portion is a second ballast element in series with said lamp.

3. A dimmer as set forth in claim 1, wherein said ballast means includes a first ballast element in series with said lamp and said gated bypass means and wherein said reactor portion is a second ballast element connected in parallel with the series combination of said gated bypass means and said first ballast element.

4. A dimmer as set forth in claim 1, wherein said gated bypass means is a triac.

5. A dimmer as set forth in claim 1, wherein said gate source voltage means is derived from a voltage in phase with the voltage supplied by said ac power distribution line, and amplitude regulated so that it cannot render said gated by-pass means conductive when the voltage across said reactor portion is no longer in polarity phase with the current therethrough.

6. A dimmer as set forth in claim 5 wherein said amplitude regulation is provided by a pair of cathode-tocathode connected zener diodes for shifting the amplitude of the voltage in phase with the power distribution voltage so that it reverses polarity no later than the voltage across said reactor reverses in polarity.

7. A dimmer as set forth in claim 1, wherein the voltage from said gate source voltage means is derived from a voltage having a phase leading the voltage supplied by said ac power distribution line such that it reverses polarity no later than the voltage across said reactor reverses polarity, thereby preventing the render- 5 ing of said gated bypass means conductive when the voltage across said reactor portion is no longer in polar ity phase with the current therethrough.

8. A dimmer as set forth in claim 7, wherein the ac power distribution line is part of a three phase power system, and the voltage from said gate source voltage means is derived from a voltage from a voltage of a phase line of the power system leading the voltage across said ballast means and lamp.

9. A dimmer as set forth in claim l, and including at least one additional ballast means and lamp connectable to the ac power distribution line, said additional ballast means including a reactor portion, and additional gated bypass means for providing bypass current around said reactor portion of said additional ballast means, said controllable gate source voltage means operably connected to said additional gated bypass means for controllably rendering it conductive, and thereby bypassing said reactor portion of said additional ballast, through a time range when the current through said reactor portion of said additional ballast and the voltage thereacross are of the same polarity.

M). A dimmer as described in claim 1, wherein said controllable gate voltage means includes switch means operable when a predetermined voltage threshold value thereof is exceeded; and variable source voltage means connected to said switch means for producing an amplitude controllable voltage substantially in phase with the line voltage, the time the amplitude of the controllable voltage reaching the threshold value of said switch means determining the gating on of said bypass means. 11. A dimmer as described in claim 1, wherein said controllable gate voltage means includes switch means operable when an applied voltage reduces below a predetermined value, the occurrence of said value being set to occur before the voltage across the reactor portion changes polarity with respect to the line current. 12. A dimmer as described in claim 1, wherein said controllable gate voltage means includes first switch means operable when a predetermined voltage threshold value thereof is exceeded; variable source voltage means connected to said switch means for producing an amplitude controllable voltage substantially in phase with the line voltage, the time the amplitude of the controllable voltage reaching the threshold value of said switch means determining the gating on of said bypass means; and second switch means operably connected to said variable source voltage means and closeably operable when the amplitude of the controllable voltage reduces below a predetermined value, the occurrence of said value occurring before the voltage across the reactor portion changes polarity with respect to the line current. 13. A dimmer as described in claim 1, wherein said controllable gate voltage means includes a transformer connected across the ac power distribution line;

a full wave bridge rectifier connected to the secondary of said transformer; and

a variable resistance connected across the dc terminals of said rectifier.

14. In combination with a plurality of high intensity gas discharge lamps, a dimmer circuit for controlling the brightnesses thereof, comprising I a plurality of separate ballast means connected to each of the lamps and connectable to an ac power distribution line,

each of said ballast means including a reactor portron,

separate gated bypass means for respectively providing bypass current around said reactor portion of each of said plurality of ballast means,

commonly controllable gate source voltage means operably connected to each of said gated bypass means for controllably rendering said gated bypass means conductive, and thereby simultaneously bypassing said reactor portion of each of said ballasts, through a time range when the current through said reactor portions and the voltages thereacross are respectively of the same polarity.

15. A dimmer circuit as set forth in claim 14, wherein each of said gate source voltage means is derived from a voltage in phase with the voltage supplied by said ac power distribution line, and amplitude regulated so that it cannot render said operably related gated bypass means conductive when the voltage across said reactor portion operably related thereto is no longer in polarity phase with the current therethrough.

16. A dimmer as set forth in claim 15, wherein the ac power distribution line is part of a multiphase power system, and wherein each of said gate source voltage means is derived from a voltage in phase with the voltage supplied by a separate phase line of the ac power distribution system.

17. A dimmer circuit as set forth in claim 15, wherein each of said gate source voltage means includes a gated bidirectional means furnished with voltage in phase with the ac power distribution line, and variable voltage control means operably connected to the gate of said gated bidirectional means for rendering said gated bidirectional means conductive.

18. A dimmer circuit as set forth in claim 17, wherein each of said variable voltage control means includes a bridge driven in phase with the ac power distribution and having dc terminals for external connection, a variable load connected between a first and a second of said bridges at said terminals, said remaining bridges being connected in series at their terminals so that all of said bridges are in series and with said variable load, the setting of said variable load determining the output voltage for each of said bridges for determining the time within said time range when the output from its operably connected variable voltage control means reaches a predetermined level for rendering its operably related gated bidirectional means conductive.

19. A dimmer for controlling the brightness of at least one high intensity, gas discharging lamp, comprising first and second inductive means connected in series with said lamp, said series combination being connectable to an ac power distribution line;

. 6 first gated bilaterally-conductive semiconductor means connected across said second inductive means, the timing of gate voltage applied thereto determining the amount of current therethrough; and

controllable gate source voltage means, including transformer means for producing a stepped-down,

controllable voltage in phase with said line voltage;

a semiconductor, bilateral switch connected for application of said controllable voltage, said switch closing when the amplitude of said applied controllable voltage exceeds a predetermined amplitude;

second grated bilaterally-conductive semiconductor means gated on by the closing of said bilateral switch to permit passage of current from said variable voltage control means; and bidirectional voltage regulating means connected in series with said second gated bilaterally-conductive semiconductor means for maintaining a predetermined voltage thereacross when the voltage threshold level is exceeded, the output from said voltage breakdown means being applied as the gate voltage to said first gated bilaterally-conductive semiconductor means. 20. A dimmer for controlling the brightness of at least one high intensity gas discharge lamp, comprising first and second inductive means connected in parallel to each other and in series with said lamp, said combination being connectable to an ac power distribution line;

first gated bilaterally-conductive semiconductor means connected in series with said second inductive means, the timing of gate voltage applied thereto determining the amount of current therethrough; and

controllable gate source voltage means, including variable voltage control means for producing a stepped-down, controllable voltage in phase with said line voltage,

a semiconductor, bilateral switch connected for application of said controllable voltage, said switch closing when the amplitude of said applied controllable voltage exceeds a predetermined amplitude,

second gated bilaterally-conductive semiconductor means gated on by the closing of said bilateral switch to permit passage of current from said variable voltage control means, and

bidirectional voltage regulating means connected in series with said second gated bilaterally-conductive semiconductor means for maintaining a predetermined voltage thereacross when the voltage threshold level is exceeded, the output from said voltage breakdown means being applied as the gate voltage to said first gated bilaterally-conductive semiconductor means.

21. A dimmer for controlling the brightness of at least one high intensity gas discharge lamp, comprising autotransformer means connected across the lamp;

a reactor connected between the primary and secondary of said autotransformer means, said primary and reactor being connectable to an ac power distribution line;

a first gated bilaterally-conductive semiconductor means connected to at least partially bypass said reactor, the timing of gate voltage applied thereto 13 14 determining the amount of current therethrough; said ballast means including a reactor portion, and gated bypass means for providing at least partial bycontrollable gate source voltage means, including pass of current around said reactor portion of said variable voltage control means for producing a b ll t a a d PP Controllable Voltage in Phase with controllable gate source voltage means operably con- Sald lme V0ltage, nected to said gated bypass means for controllably a semiconductor, bilateral switch connected for aprendering said gated bypass means conductive, and plication of said controllable voltage, said switch thereby bypassing Said reactor portion f Said closing when the amplitude of said applied conlast tmuable voltage exceeds a predetermined ampli' 23. In combination with a high intensity gas discharge tude lam a dimmer circuit for controlhn the bri htness second gated bilaterally-conductive semiconductor thergof Comprising g g gated by the closmg of Said bllater? ballast means connected to the lamp and connectable switch to permit passage of current from said to an ac power distribution line variable voltage control means, and bidirectional voltage regulating means connected in i ballast means mcludmg first and Second reac' series with said second gated bilaterally-conductive or por ions gated bypass means for providing at least partial bysemiconductor means for maintaining a predetermined voltage thereacross when the voltage threshpass of curre m one of Said first and Second reactor portions of said ballast means, and

old level is exceeded, the output from said voltage breakdown means being applied as the gate voltage controllabk a Source Voltage means p y to said first gated bilaterally-conductive semicon- "acted to Said gated yp means for comfonably d t means rendering said gated bypass means conductive, and

22. In combination with a high intensity gas discharge thereby yp i g Said reactor P t f Sa ballamp, a dimmer circuit for controlling the brightness ast, ug a t rang h n the urr nt thereof, comprising: through said reactor portion and the voltage thereballast means connected to the lamp and connectable across are of substantially the same polarity.

to an ac power distribution line,

' 230 V UNl'iEl) STATES PATENT GFFICE CERTEFECATE 9F CQRRECTIGN Patent No. 3,816,794 Dated June 11, 1974 Q i Invent r(3) Carl R- Snyder It is certified that error appears in the above-identified patent and that: said Letters Patent are hereby corrected as shown below:

should read --conductive;

Colv ll, line Col, 12, line Abstract, line 18, conuctve'" Col". 7, line -59, "lanp" should read --lamp-. 60, "discharging" should read -discha'rge. l2, "grated" should read -gated--.

Signed and sealed this 18th day of February 1975.

(SEAL) Attest: v c.' MARSHALL DANN RUTH c. MASON Attesting Officer- Commissioner of Patents and Trademarks 

1. In combination with a high intensity gas discharge lamp, a dimmer circuit for controlling the brightness thereof, comprising ballast means connected to the lamp and connectable to an ac power distribution line, said ballast means including a reactor portion, gated bypass means for providing at least partial bypass of current around said reactor portion of said ballast means, and controllable gate source voltage means operably connected to said gated bypass means for controllably rendering said gated bypass means conductive, and thereby bypassing said reactor portion of said ballast, through a time range when the current through said reactor portion and the voltage thereacross are of the same polarity.
 2. A dimmer as set forth in claim 1, wherein said ballast means includes a first ballast element in series with said lamp and wherein said reactor portion is a second ballast element in series with said lamp.
 3. A dimmer as set forth in claim 1, wherein said ballast means includes a first ballast element in series with said lamp and said gated bypass means and wherein said reactor portion is a second ballast element connected in parallel with the series combination of said gated bypass means and said first ballast element.
 4. A dimmer as set forth in claim 1, wherein said gated bypass means is a triac.
 5. A dimmer as set forth in claim 1, wherein said gate source voltage means is derived from a voltage in phase with the voltage supplied by said ac power distribution line, and amplitude regulated so that it cannot render said gated by-pass means conductive when the voltage across said reactor portion is no longer in polarity phase with the current therethrough.
 6. A dimmer as set forth in claim 5 wherein said amplitude regulation is provided by a pair of cathode-to-cathode connected zener diodes for shifting the amplitude of the voltage in phase with the power distribution voltage so that it reverses polarity no later than the voltage across said reactor reverses in polarity.
 7. A dimmer as set forth in claim 1, wherein the voltage from said gate source voltage means is derived from a voltage having a phase leading the voltage supplied by said ac power distribution line such that it reverses polarity no later than the voltage across said reactor reverses polarity, thereby preventing the rendering of said gated bypass means conductive when the voltage across said reactor portion is no longer in polarity phase with the current therethrough.
 8. A dimmer as set forth in claim 7, wherein the ac power distribution line is part of a three phase power system, and the voltage from said gate source voltage means is derived from a voltage from a voltage of a phase line of the power system leading the voltage across said ballast means and lamp.
 9. A dimmer as set forth in claim 1, and including at least one additional ballast means and lamp connectable to the ac power distribution line, said additional ballast means including a reactor portion, and additional gated bypass means for providing bypass current around said reactor portion of said additional ballast means, said controllable gate source voltage means operably connected to said additional gated bypass means for controllably rendering it conductive, and thereby bypassing said reactor portion of said additional ballast, through a time range when the current through said reactor portion of said additional ballast and the voltage thereacross are of the same polarity.
 10. A dimmer as described in claim 1, wherein said controllable gate voltage means includes switch means operable when a predetermined voltage threshold value thereof is exceeded; and variable source voltage means connected to said switch means for producing an amplitude controllable voltage substantially in phase with the line voltage, the time the amplitude of the controllable voltage reaching the threshold value of said switch means determining the gating on of said bypass means.
 11. A dimmer as described in claim 1, wherein said controllable gate voltage means includes switch means operable when an applied voltage reduces below a predetermined value, the occurrence of said value being set to occur before the voltage across the reactor portion changes polarity with respect to the line current.
 12. A dimmer as described in claim 1, wherein said controllable gate voltage means includes first switch means operable when a predetermined voltage threshold value thereof is exceeded; variable source voltage means connected to said switch means for producing an amplitude controllable voltage substantially in phase with the line voltage, the time the amplitude of the controllable voltage reaching the threshold value of said switch means determining the gating on of said bypass means; and second switch means operably connected to said variable source voltage means and closeably operable when the amplitude of the controllable voltage reduces below a predetermined value, the occurrence of said value occurring before the voltage across the reactor portion changes polarity with respect to the line current.
 13. A dimmer as described in claim 1, wherein said controllable gate voltage means includes a transformer connected across the ac power distribution line; a full wave bridge rectifier connected to the secondary of said transformer; and a variable resistance connected across the dc terminals of said rectifier.
 14. In combination with a plurality of high intensity gas discharge lamps, a dimmer circuit for controlling the brightnesses thereof, comprising a plurality of separate ballast means connected to each of the lamps and connectable to an ac poWer distribution line, each of said ballast means including a reactor portion, separate gated bypass means for respectively providing bypass current around said reactor portion of each of said plurality of ballast means, commonly controllable gate source voltage means operably connected to each of said gated bypass means for controllably rendering said gated bypass means conductive, and thereby simultaneously bypassing said reactor portion of each of said ballasts, through a time range when the current through said reactor portions and the voltages thereacross are respectively of the same polarity.
 15. A dimmer circuit as set forth in claim 14, wherein each of said gate source voltage means is derived from a voltage in phase with the voltage supplied by said ac power distribution line, and amplitude regulated so that it cannot render said operably related gated bypass means conductive when the voltage across said reactor portion operably related thereto is no longer in polarity phase with the current therethrough.
 16. A dimmer as set forth in claim 15, wherein the ac power distribution line is part of a multiphase power system, and wherein each of said gate source voltage means is derived from a voltage in phase with the voltage supplied by a separate phase line of the ac power distribution system.
 17. A dimmer circuit as set forth in claim 15, wherein each of said gate source voltage means includes a gated bidirectional means furnished with voltage in phase with the ac power distribution line, and variable voltage control means operably connected to the gate of said gated bidirectional means for rendering said gated bidirectional means conductive.
 18. A dimmer circuit as set forth in claim 17, wherein each of said variable voltage control means includes a bridge driven in phase with the ac power distribution and having dc terminals for external connection, a variable load connected between a first and a second of said bridges at said terminals, said remaining bridges being connected in series at their terminals so that all of said bridges are in series and with said variable load, the setting of said variable load determining the output voltage for each of said bridges for determining the time within said time range when the output from its operably connected variable voltage control means reaches a predetermined level for rendering its operably related gated bidirectional means conductive.
 19. A dimmer for controlling the brightness of at least one high intensity, gas discharging lamp, comprising first and second inductive means connected in series with said lamp, said series combination being connectable to an ac power distribution line; first gated bilaterally-conductive semiconductor means connected across said second inductive means, the timing of gate voltage applied thereto determining the amount of current therethrough; and controllable gate source voltage means, including transformer means for producing a stepped-down, controllable voltage in phase with said line voltage; a semiconductor, bilateral switch connected for application of said controllable voltage, said switch closing when the amplitude of said applied controllable voltage exceeds a predetermined amplitude; second grated bilaterally-conductive semiconductor means gated on by the closing of said bilateral switch to permit passage of current from said variable voltage control means; and bidirectional voltage regulating means connected in series with said second gated bilaterally-conductive semiconductor means for maintaining a predetermined voltage thereacross when the voltage threshold level is exceeded, the output from said voltage breakdown means being applied as the gate voltage to said first gated bilaterally-conductive semiconductor means.
 20. A dimmer for controlling the brightness of at least one high intensity gas discharge lamp, comprising first and second inductive means connected in parallel to each other anD in series with said lamp, said combination being connectable to an ac power distribution line; first gated bilaterally-conductive semiconductor means connected in series with said second inductive means, the timing of gate voltage applied thereto determining the amount of current therethrough; and controllable gate source voltage means, including variable voltage control means for producing a stepped-down, controllable voltage in phase with said line voltage, a semiconductor, bilateral switch connected for application of said controllable voltage, said switch closing when the amplitude of said applied controllable voltage exceeds a predetermined amplitude, second gated bilaterally-conductive semiconductor means gated on by the closing of said bilateral switch to permit passage of current from said variable voltage control means, and bidirectional voltage regulating means connected in series with said second gated bilaterally-conductive semiconductor means for maintaining a predetermined voltage thereacross when the voltage threshold level is exceeded, the output from said voltage breakdown means being applied as the gate voltage to said first gated bilaterally-conductive semiconductor means.
 21. A dimmer for controlling the brightness of at least one high intensity gas discharge lamp, comprising autotransformer means connected across the lamp; a reactor connected between the primary and secondary of said autotransformer means, said primary and reactor being connectable to an ac power distribution line; a first gated bilaterally-conductive semiconductor means connected to at least partially bypass said reactor, the timing of gate voltage applied thereto determining the amount of current therethrough; and controllable gate source voltage means, including variable voltage control means for producing a stepped-down, controllable voltage in phase with said line voltage, a semiconductor, bilateral switch connected for application of said controllable voltage, said switch closing when the amplitude of said applied controllable voltage exceeds a predetermined amplitude, second gated bilaterally-conductive semiconductor means gated on by the closing of said bilateral switch to permit passage of current from said variable voltage control means, and bidirectional voltage regulating means connected in series with said second gated bilaterally-conductive semiconductor means for maintaining a predetermined voltage thereacross when the voltage threshold level is exceeded, the output from said voltage breakdown means being applied as the gate voltage to said first gated bilaterally-conductive semiconductor means.
 22. In combination with a high intensity gas discharge lamp, a dimmer circuit for controlling the brightness thereof, comprising: ballast means connected to the lamp and connectable to an ac power distribution line, said ballast means including a reactor portion, gated bypass means for providing at least partial bypass of current around said reactor portion of said ballast means, and controllable gate source voltage means operably connected to said gated bypass means for controllably rendering said gated bypass means conductive, and thereby bypassing said reactor portion of said ballast.
 23. In combination with a high intensity gas discharge lamp, a dimmer circuit for controlling the brightness thereof, comprising: ballast means connected to the lamp and connectable to an ac power distribution line, said ballast means including first and second reactor portions, gated bypass means for providing at least partial bypass of current around one of said first and second reactor portions of said ballast means, and controllable gate source voltage means operably connected to said gated bypass means for controllably rendering said gated bypass means conductive, and thereby bypassing said reactor portion of said ballast, through a time range when the curRent through said reactor portion and the voltage thereacross are of substantially the same polarity. 